Asrij/OCIAD1 depletion reduces inflammatory microglial activation and ameliorates Aβ pathology in an Alzheimer's disease mouse model

Background Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles, neuroinflammation, and glial activation. Asrij/OCIAD1 (Ovarian Carcinoma Immunoreactive Antigen Domain containing protein 1) is an AD-associated factor. Increased Asrij levels in the brains of AD patients and mouse models are linked to the severity of neurodegeneration. However, the contribution of Asrij to AD progression and whether reducing Asrij levels is sufficient to mitigate Aβ pathology in vivo is unclear.

To explore the impact of Asrij on AD pathology, we deleted asrij in the APP/PS1 mouse model of AD and analyzed the effects on AD hallmarks. We used the Morris water maze and open field test to assess behavioral performance. Using immunohistochemistry and biochemical analyses, we evaluated Aβ plaque load, neuronal and synaptic damage, and gliosis. Further, we utilized confocal microscopy imaging, flow cytometry and RNA sequencing analysis to comprehensively investigate changes in microglial responses to Aβ pathology upon Asrij depletion.

Asrij depletion ameliorates cognitive impairments, Aβ deposition, neuronal and synaptic damage, and reactive astrogliosis in the AD mouse. Notably, Asrij-deficient microglia exhibit reduced plaque-associated proliferation and decreased phagocytic activation. Transcriptomic analyses of AD microglia reveal upregulation of energy metabolism pathways and downregulation of innate immunity and inflammatory pathways upon Asrij depletion. Mechanistically, loss of Asrij increases mitochondrial activity and impedes the acquisition of a pro-inflammatory disease-associated microglia (DAM) state. Reduced levels of pro-inflammatory cytokines and decreased STAT3 and NF-κB activation indicate protective changes in AD microglia. Taken together, our results suggest that increased Asrij levels reported in AD, may suppress microglial metabolic activity and promote inflammatory microglial activation, thereby exacerbating AD pathology.

In summary, we show that Asrij depletion ameliorates Aβ pathology, neuronal and synaptic damage, gliosis, and improves behavioral performance in APP/PS1 mice. This supports that Asrij exacerbates the AD pathology. Mechanistically, Asrij is critical for the development of DAM and promotes neuroinflammatory signaling activation in microglia, thus restricting neuroprotective microglial responses. Hence, reducing Asrij in this context may help retard AD. Our work positions Asrij as a critical molecular regulator that links microglial dysfunction to AD pathogenesis. Competing Interest Statement The authors have declared no competing interest. Abbreviations - AD - Alzheimer’s disease - Aβ - Amyloid beta - GWAS - Genome-wide association studies - OCIAD1 - Ovarian Carcinoma Immunoreactive Antigen Domain protein 1 - GSK3β - Glycogen synthase kinase 3 beta - DAM - Disease-associated microglia - WT - Wild type - KO - Knockout - PCR - Polymerase chain reaction - JNCASR - Jawaharlal Nehru Centre for Advanced Scientific Research - OFT - Open field test - MWM - Morris water maze - PBS - Phosphate-buffered saline - PFA - Paraformaldehyde - RNA - Ribonucleic acid - RT - Room temperature - FBS - Fetal bovine serum - DAPI - 4′,6-diamidino-2-phenylindole - HEPES - 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - EDTA - Ethylenediaminetetraacetic acid - DTT - Dithiothreitol - PMSF - Phenylmethylsulfonyl fluoride - SDS - Sodium dodecyl sulfate - HRP - Horseradish peroxidase - ECL - Clarity western enhanced chemiluminescence - HBSS - Hanks’ balanced salt solution - BSA - Bovine serum albumin - DPBS - Dulbecco’s phosphate-buffered saline - MACS - Magnetic-activated cell sorting - FACS - Fluorescence-activated cell sorting - TMRM - Tetramethylrhodamine, Methyl Ester, Perchlorate - FSC-A - Forward scatter area - SSC-A - Side scatter area - FSC-H - Forward scatter height - SSC-W - Side scatter width - MFI - Median fluorescence intensity - IMDM - Iscove’s modified Dulbecco’s medium - ELISA - Enzyme-linked immunosorbent assay - RT-qPCR - Reverse transcription-quantitative polymerase chain reaction - QC - Quality control - rRNA - ribosomal RNA - PCA - Principal component analysis - MSigDB - Molecular signatures database - SEM - Standard error of mean - ANOVA - Analysis of variance - ThioS - Thioflavin S - APP - Amyloid precursor protein - CTF - Carboxy-terminal fragments - LAMP1 - Lysosomal-associated membrane protein 1 - PSD95 - Post synaptic density 95 - GFAP - Glial fibrillary acidic protein - S100B - S100 calcium-binding protein B - IBA1 - Ionized calcium-binding adapter molecule 1 - CD68 - Cluster of differentiation 68 - RNA-seq - RNA sequencing - GO - Gene ontology - DEG - Differentially expressed genes - TMRM - Tetramethylrhodamine, Methyl Ester, Perchlorate - ROS - Reactive oxygen species - mTOR - Mammalian target of rapamycin - MGnD - Microglial neurodegenerative phenotype - CLEC7A - C-Type lectin domain containing 7A - TMEM119 - Transmembrane protein 119 - IRM - Interferon response microglia - ISG - Interferon-stimulated genes - MHC - Major histocompatibility complex - IL-6 - Interleukin-6 - TNF-alpha - Tumor necrosis factor α - IL-1beta - Interleukin-1β - IFN - Interferon - KEGG - Kyoto encyclopedia of genes and genomes - GAPDH - Glyceraldehyde-3-phosphate dehydrogenase - STAT3 - Signal transducer and activator of transcription 3 - NF-κB - Nuclear factor kappa-light-chain-enhancer of activated B cells - ETC - Electron transport chain - BLiSC - Bangalore Life Science Cluster